This invention relates to a cathode ray tube screen exposure device and more particularly to radiant energy source means employed in the optical system of a cathode ray tube screen exposure device.
Cathode ray tubes of the type employed in image reproduction, such as in color television applications and similar display media, conventionally utilize electron gun structures which provide one or more electron beams to effect the desired display imagery. In operation, the modulated electron beams are predeterminately scanned across the screen of the tube to provide electron impingement upon selected color-emitting phosphor configurations comprising the patterned screen disposed on the viewing panel of the tube, whereupon the transmitted color display is reproduced. Color picture tubes of this type usually employ a multi-apertured grid, mask, or other type of negative structure which is interposed between the electron gun assembly and the screen structure to provide either masking of the screen, or deflection or focusing of the electron beam or beams thereat.
In a conventional color cathode ray tube, the electron sensitive screen is usually comprised of a repetitive pattern of multitudinous dot, bar, or stripe formations of various phosphors capable of emitting, for example, green, red and blue color luminescence upon electron beam impingement. In certain tube constructions, the pattern of phosphors comprising the screen is disposed to overlay an array of multitudinous window areas of an opaque screen matrix formed on the viewing portion of the panel. The shapings or configurations of the matrix windows and the associated color phosphor patterns constituting this type of screen structure are formed in accordance with the number of electron beams utilized and with the discrete aperture configurations and operative characteristics of the grid or mask structure employed in the respective tube.
Since a vast number of color phosphor groups are required to produce a high resolution display of desired color purity, the process employed in forming both the basic window matrix, and the associated phosphor screen, must be one that is capable of accurately forming a multitude of similar discrete configurations in the screen arrangement. In a preferred method for fabricating the screen structure for a color tube, a photoprinting technique is utilized wherein the viewing panel of the tube, having an interior coating of a photosensitive resist composition disposed thereon, is positioned upon a screen exposure device and suitably photo-exposed through the related negative or multi-apertured mask by radiant energy emanating from a specifically oriented light source means within the device. Subsequent development of the numerous selectively exposed areas of the panel, produces either a first window pattern of the matrix, or in proper sequence, the associated first color phosphor pattern of the subsequently formed screen. Such photo exposure is sequentially repeated in the proper steps of the procedure to form the remaining windows in the matrix and likewise to later effect deposition of the respective color-emitting phosphor materials associated therewith to complete the fabrication of the patterned screen construction. In separately producing the matrix and the related patterned array of phosphor elements associated therewith, the light means providing the radiant energy necessary for the photo-deposition procedure, is appropriately offset from the central axis of the device during the exposure procedure for some or all of the respective exposure steps in accordance with the requirements for each of the color phosphor patterns and definitive window areas constituting the screen. For example, in forming a tri-dot screen structure a light source means is offset for each of the respective exposure operations; while in forming tri-color inline type screens, the light source means is offset from a central axis for only two of the exposure operations.
The screen exposure device, which is conventionally known in the art as a "lighthouse" usually contains an optical system comprising a light permeable refractive medium or corrective lens and an associated light source means positioned to provide the required amount of radiant or actinic energy for proper photo-exposure activation of the light sensitive coating disposed on the viewing area of the panel. For instance, to produce a desired screen pattern of both the basic matrix and the related phosphor elements of the screen structure, the components of the optical system are oriented or aligned relative to an optical axis in a manner to radiate light over the whole of the multi-apertured mask. Thus, the actinic energy traverses the apertures therein to expose discretely shaped areas, be they matrix windows or the subsequently disposed phosphor dots or stripes, on the respective sensitized screen material therebehind to thereby produce a patterned array of defined configurations having exactness in accordance with the registration requirements of the subsequent electron beam impingement in the finished tube.
A factor of prime importance in the optical system of the exposure device, is the source means of radiant energy employed therein. One common source of exposure radiation has been a mercury vapor lamp evidencing an incandescent arc of substantially elliposidal or elongated shaping. The luminescence of this arc in conjunction with the reflective means provides the sole source of radiant energy for the photo-exposure process. Consequently, to polymerize the photosensitive material with a given amount of exposure radiation, the intensity of the irradiation determines the time factor of the exposure and thereby becomes an important consideration in establishing the speed of the operation. In addition, non-uniformity of light distribution, due to changes in the shape of the incandescent arc, has been noticed during the operational life of the lamp. Accordingly, optimized exposure radiation emanating from the optical system, to provide desired uniformity of exposure, is often unattained due to the difficulty encountered in effecting minute adjustments of the exposure lamp during operation of the device. Thus, the regulation and monitoring of radiant energy output becomes a major problem in the exposure operation.